1. Field of the Invention
The present invention relates to a device for compressing a load of tires or other compressible material for improving the load density of compressible materials loaded in a shipping container.
2. State of the Art
Tires must be shipped from factories to warehouses and distributors. Typical load densities for tires shipped in a freight container are quite low. That is, although a passenger tire may be 2' (0.3 m) (metric equivalents are approximate) in diameter and 6" (15 cm) wide, the tire volume is mostly air.
How tires are loaded in the container affects the amount of unused space in a load of tires. It is generally believed that loading tires in a herringbone pattern maximizes load density. In a herringbone pattern, which FIG. 2 shows, a first tire is either laid flat (i.e., horizontal) or propped at an angle against the side wall in the front corner of a shipping container floor (as FIG. 2 shows). If the first tire is laid flat, the next tire leans against the first tire at an angle. If the first tire is propped at an angle against the wall, the next tire is placed parallel to the first. The third tire is then placed parallel to the second, and the process is repeated until the last tire reaches the other front corner to complete a first row of tires.
A second row is mounted above the first row, but each tire in the second row is angled in the opposite direction to the angle of the tires in the first row. Additional rows are added until the load reaches the top of the container, thus completing a stack or column. Next, a second row behind the first stack is started, and a new herringbone pattern is made. This continues with stacks continuing to the back of the container until the container is filled.
U.S. Pat. Nos. 4,777,781 (1988) and 4,920,729 (1990), both to Doster et al., disclose devices for compressing tires vertically to improve load density. Both devices install themselves in place before any tires are stacked in the shipping container. When the herringbone pattern reaches about 2/3 or 3/4 to the top of the container, a hydraulic ram on a tug pushes or pulls a plate over the stack down on the top row of tires of one stack. The plate thus compresses the rows below.
In the earlier patent, the compression plate is first raised to the ceiling after the tug is clamped to the ceiling but before any tires are stacked in the container. The later patent is mounted on a machine that is not a forklift, tug or other standard machine. In both devices, while the stack of tires remain compressed, other tires are loaded above the plate. The hydraulics then push the plate (or what the patent calls the "wedge") upward, which partially relieves some of the compression on the tires of the stack below the wedge and simultaneously compresses partially the tires above the wedge. When the load above and below the wedge is approximately equal, the wedge is removed from between two rows. A pusher next to the wedge holds the rows above and below the wedge while the wedge is removed. The process is repeated for all subsequent stacks.
One problem of the just-described device is the use of a two way driver for moving the wedge up and down. Because the system uses hydraulics to compress the tires below the wedge, the wedge must push against the compressed tires. Those compressed tires exert an opposite force on the wedge. To prevent that opposite force from lifting the wedge and the entire device, the device needs an overhead frame to contact the container ceiling for supporting the device between the container floor and ceiling. The overhead frame prevents the tires from pushing the entire device upward. The mechanism that moves the overhead frame against the ceiling complicates the device, however. Also, having two-way, hydraulically driven movement makes this device more complex and subject to increased maintenance expenses.
Further, the amount that the device compresses tires below the wedge can vary with different operators. An operator using the device's hydraulics may over- or under-compress the tires. Over-compression may damage tires. Too little compression results in insufficient volume reduction.
When the wedge of the prior art device is removed from the rows of tires, there is a tendency for the tire stack to bow outward or fall over. The prior art holds the rows of tires immediately above and below the wedge as the wedge is removed, but nothing secures the rows lower in the stack.
In U.S. Pat. No. 4,777,781, where the compression plate is first raised to the ceiling, loaders must work under the plate and in front of the machine. This is undesirable.